There is an ongoing discussion over at I'd Rather Be Killing Monsters and on Tim's google+ about acting and roleplaying.
I think that, if when I started playing and, if I knew that the preconception was that D&D/RPgs were acting, I wouldn't have gotten involved. I have always been very shy and don't like to draw attention to myself. Acting is an extremely unappealing venture to my mind. However, that was not the case and went in without any preconceived notions.
For me, it is me being me in a fantasy setting. I am my character, as myself, just with parameters. Alys, my thief, has a high charisma. I don't. I usually come off as snobby (because I am shy). So rather than try to be all charming in roleplaying I will just rely on the dice. Also, I am the only American sitting at a table full of Brits with their lovely educated accents but I am not going to affect a British accent for the sake of continuity.
I will be the only American in the village.
Just my two copper pieces worth.